Why is there suddenly a different seekbar in fullscreen?

Why am I seeing tearing in the video?

The video display is experiencing a synchronisation issue, try enabling V-Sync by pressing V. If you have more than one monitor connected make sure you extend the screen instead of duplicating it.

Why am I seeing strange glitches in the video?

Hardware acceleration is most likely not working correctly. Try going to Options → Internal Filters, click Video decoder, set “Hardware decoder to use:” to “None” and then reload the video (Ctrl+E or manually). If this does not solve your issue, and your video plays correctly in other video players then please make a bug report.

Will MPC-HC support Windows RT or Metro?

Supporting these new platforms require many changes and this is simply not possible for us in the near future, with the current manpower.